The raw juice extracted from vegetable products can be both alcoholic and non-alcoholic raw juices, for example raw juice from fruit, grapes, berries or other fruits and vegetables, as well as oil seeds for extracting oil. Also products derived from several vegetable products, for example beers in particular in connection with beer recovery from fermenter or tank storage yeast, are suitable.
Through WO 89/02708 it is known, how to proceed in the clarification of liquids with a high proportion of solids in the retentate circulation cycle. Thus the objective is pursued to improve the filtration yield of the diaphragms significantly.
Because of the high proportion of solids in the retentate circulation cycle, the danger exists in such units that the filtration modules of the cross flow filtration device become clogged. Particularly when the unit is suddenly shut down, as for example when there is a power failure, or an interruption of control air for the pneumatically operated devices etc., all retentate conduits of the cross flow filtration system must be flushed out as quickly as possible. If this does not take place immediately, the viscosity of the retentate increases, because the retentate is athixotropic liquid and the liquid is no longer being moved when the retentate circulating pump stops. As a consequence the filtration modules possibly can no longer be flushed out with flushing agents or have to be cleaned out conduit by conduit at great expense mechanically, but most often by hand. Generally, this is only possible in modules with wide conduits, narrow conduits become clogged irreversibly.
This problem is even further complicated in that an operation often has to be performed at a higher than average proportion of cloudiness in the retentate cycle to operate the cross flow filtration with drastically increased filtration yield.
To avoid these drawbacks, it is known, when the unit shuts down, to feed water to the retentate cycle to flush the modules. The delivery of water takes place upstream from the circulating pump for the retentate and is carried out in a known way with the help of open/closed fittings. With the feeding of water the retentate is diluted, so that the viscosity decreases and the unit can then be started up again normally.
For the retentate feeding to the module or module group, i.e. several modules connected in series, it is known to supply the individual module groups or the individual modules asymmetrically for the purpose of running the pipeline in a simple way. For this purpose several side pipelines branch off from the main line one after another to the individual module groups or to the individual modules. The same is also true for the retentate discharge from the module groups. Another, known design uses three modules, which are supplied symmetrically in three individual pipelines by a branching of the main line.
The addition of water as a flushing agent to the retentate cycle and the known method of conveying the retentate to the module group, in particular the symmetrical inflow and discharge, can contribute in simple cases to lessening the danger of the clogging of the modules. If however, as in the present case, the unit is being run with a very high proportion of solids in the retentate cycle, these known measures, in the above emergency situations, no longer suffice to flush out the filtration modules with water.